Changing scene by clicking on a game object

Hello everyone, firstly I apologize for my basic question, I'm a begginer with programming and can't get to make this simple action! I have a scene in which I placed four objects, and I want to change to a different scene every time the user presses a game object. I got to do it without a problem by pressing different keys, but when I want to do it by clicking on the objects I get really lost. I tried creating an int that changes value when the user presses the object, but I'm having problems accesing that int from another script. Maybe there is a simple way and I'm not realising it.. This is the code I used for changing scenes with the keyboard:

 using UnityEngine;
 using System.Collections;
 
 public class SceneManager : MonoBehaviour
 {
 
     static SceneManager Instance;
 
     void Start()
     {
         if (Instance != null)
         {
             GameObject.Destroy(gameObject);
         }
         else
         {
             GameObject.DontDestroyOnLoad(gameObject);
             Instance = this;
         }
 
     }
 
     void Update()
     {
         if (Input.GetKeyUp(KeyCode.UpArrow))
         {
             Application.LoadLevel("2");
         }
         if (Input.GetKeyUp(KeyCode.DownArrow))
         {
             Application.LoadLevel("Demo");
         }
     }
 }

Thank you in advance!